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+# Rack Power (Phase 2) Implementation Plan
+
+> **For agentic workers:** REQUIRED SUB-SKILL: Use superpowers:subagent-driven-development (recommended) or superpowers:executing-plans to implement this plan task-by-task. Steps use checkbox (`- [ ]`) syntax for tracking.
+
+**Goal:** Add power-distribution data (`power:` feeds + PDU files) to the rack pipeline, validate it, and render a mermaid power graph on the generated rack page — reusing every Phase 1 mechanism.
+
+**Architecture:** Extend the existing `scripts/gen_rack.py` with `validate_power` (rule 3 from the spec) and `render_power` (a `flowchart LR` with the outlet number as the edge label); insert a `## Power` section into `render_page`. PDU files are 0U `left`/`right` items that Phase 1 already renders as side-rails and `gen_overview.py` already lists. Pull the mermaid superfences fence forward into `mkdocs.yml` so the graph renders.
+
+**Tech Stack:** Python 3 (stdlib + PyYAML only), pytest, MkDocs Material, Forgejo Actions CI.
+
+**Spec:** `notes/dev/specs/2026-06-24-rack-power-design.md`.
+
+## Global Constraints
+
+- Scripts use **stdlib + PyYAML only**; deterministic and offline (copy `gen_rack.py`/`gen_overview.py` style). No randomness/time in generated output.
+- `re` and `yaml` are already imported in `scripts/gen_rack.py`; do not add new imports.
+- Validation failures raise `SchemaError`; `generate` prints `ERROR: …` to stderr and returns `1`, **writing nothing** on failure (existing Phase 1 behaviour).
+- Generated files keep the existing `_Auto-generated … do not edit by hand_` banner.
+- PDU files are **0U**: `rack_face: left|right`, **no** `rack_u`/`u_height`, and a positive-int `outlets`.
+- Power data added here is **provisional placeholder data** (like the existing `mfNN` U positions), not real values.
+- The Makefile `docs-check` and CI drift step already diff the whole `docs/infrastructure/racks/` dir — **do not edit** `Makefile`, `.forgejo/workflows/docs.yml`, or `scripts/overview_config.yml`.
+- `mkdocs build --strict` must pass; `make docs-check` must exit 0 after regeneration.
+
+---
+
+### Task 1: `validate_power` — rule 3 validation (TDD)
+
+Add PDU lookup + power-feed validation and wire it into `generate`. This task is testable on validation alone (no rendering needed).
+
+**Files:**
+- Modify: `scripts/gen_rack.py` (add `_pdu_index`, `validate_power`; call in `generate`)
+- Modify: `tests/test_gen_rack.py` (append tests)
+
+**Interfaces:**
+- Consumes: `SchemaError`, the `item()`/`_write_item` test helpers, `generate`.
+- Produces:
+  - `_pdu_index(items: list[dict]) -> dict[str, dict]` — `{hostname: fm}` for `kind == "pdu"` items.
+  - `validate_power(items: list[dict]) -> None` — raises `SchemaError` on a bad PDU `outlets` declaration or a bad `power` feed.
+
+- [ ] **Step 1: Append failing tests to `tests/test_gen_rack.py`**
+
+```python
+def test_validate_power_accepts_valid_feed():
+    items = [
+        item(hostname="pdu01", kind="pdu", rack_face="left", outlets=8),
+        item(hostname="mf00", rack_u=1, u_height=1, rack_face="front",
+             power=[{"pdu": "pdu01", "outlet": 1}]),
+    ]
+    gen_rack.validate_power(items)
+
+
+def test_validate_power_rejects_unknown_pdu():
+    items = [item(hostname="mf00", rack_u=1, u_height=1, rack_face="front",
+                  power=[{"pdu": "ghost", "outlet": 1}])]
+    with pytest.raises(gen_rack.SchemaError):
+        gen_rack.validate_power(items)
+
+
+def test_validate_power_rejects_non_pdu_target():
+    items = [
+        item(hostname="sw01", kind="switch", rack_u=1, u_height=1,
+             rack_face="front"),
+        item(hostname="mf00", rack_u=2, u_height=1, rack_face="front",
+             power=[{"pdu": "sw01", "outlet": 1}]),
+    ]
+    with pytest.raises(gen_rack.SchemaError):
+        gen_rack.validate_power(items)
+
+
+def test_validate_power_rejects_outlet_over_count():
+    items = [
+        item(hostname="pdu01", kind="pdu", rack_face="left", outlets=8),
+        item(hostname="mf00", rack_u=1, u_height=1, rack_face="front",
+             power=[{"pdu": "pdu01", "outlet": 9}]),
+    ]
+    with pytest.raises(gen_rack.SchemaError):
+        gen_rack.validate_power(items)
+
+
+def test_validate_power_rejects_outlet_zero():
+    items = [
+        item(hostname="pdu01", kind="pdu", rack_face="left", outlets=8),
+        item(hostname="mf00", rack_u=1, u_height=1, rack_face="front",
+             power=[{"pdu": "pdu01", "outlet": 0}]),
+    ]
+    with pytest.raises(gen_rack.SchemaError):
+        gen_rack.validate_power(items)
+
+
+def test_validate_power_rejects_malformed_entry():
+    items = [
+        item(hostname="pdu01", kind="pdu", rack_face="left", outlets=8),
+        item(hostname="mf00", rack_u=1, u_height=1, rack_face="front",
+             power=["pdu01"]),
+    ]
+    with pytest.raises(gen_rack.SchemaError):
+        gen_rack.validate_power(items)
+
+
+def test_validate_power_rejects_pdu_without_outlets():
+    items = [
+        item(hostname="pdu01", kind="pdu", rack_face="left"),
+        item(hostname="mf00", rack_u=1, u_height=1, rack_face="front",
+             power=[{"pdu": "pdu01", "outlet": 1}]),
+    ]
+    with pytest.raises(gen_rack.SchemaError):
+        gen_rack.validate_power(items)
+
+
+def test_generate_returns_1_on_bad_power_ref(tmp_path):
+    hw = tmp_path / "hardware"
+    out = tmp_path / "out"
+    hw.mkdir()
+    _write_item(
+        hw,
+        "mf00",
+        "---\nhostname: mf00\nkind: server\nstatus: in-use\n"
+        "rack: rack01\nrack_u: 1\nu_height: 1\nrack_face: front\n"
+        "power:\n  - { pdu: ghost, outlet: 1 }\n---\n",
+    )
+    rc = gen_rack.generate(hw, out)
+    assert rc == 1
+    assert not (out / "rack01.md").exists()
+```
+
+- [ ] **Step 2: Run to verify failure**
+
+Run: `pytest tests/test_gen_rack.py -q`
+Expected: FAIL — `AttributeError: module 'gen_rack' has no attribute 'validate_power'`.
+
+- [ ] **Step 3: Add `_pdu_index` and `validate_power` after `check_overlaps` in `scripts/gen_rack.py`**
+
+```python
+def _pdu_index(items: list[dict]) -> dict[str, dict]:
+    """Map hostname -> frontmatter for every kind:pdu item."""
+    return {
+        fm.get("hostname"): fm
+        for fm in items
+        if fm.get("kind") == "pdu"
+    }
+
+
+def validate_power(items: list[dict]) -> None:
+    """Validate PDU outlet declarations and `power` feeds within one rack.
+
+    Rule 3: every power[].pdu resolves to a kind:pdu file, and outlet is
+    within that PDU's `outlets` count.
+    """
+    pdus = _pdu_index(items)
+    for name, fm in pdus.items():
+        outlets = fm.get("outlets")
+        if not isinstance(outlets, int) or outlets < 1:
+            raise SchemaError(
+                f"{name}: kind:pdu must declare a positive integer 'outlets'"
+            )
+    for fm in items:
+        feeds = fm.get("power")
+        if feeds is None:
+            continue
+        name = fm.get("hostname", "?")
+        if not isinstance(feeds, list):
+            raise SchemaError(f"{name}: power must be a list")
+        for feed in feeds:
+            if not isinstance(feed, dict):
+                raise SchemaError(f"{name}: power entry must be a mapping")
+            pdu = feed.get("pdu")
+            outlet = feed.get("outlet")
+            if not isinstance(pdu, str) or not pdu:
+                raise SchemaError(f"{name}: power entry needs a non-empty 'pdu'")
+            if not isinstance(outlet, int):
+                raise SchemaError(
+                    f"{name}: power entry for {pdu} needs an integer 'outlet'"
+                )
+            target = pdus.get(pdu)
+            if target is None:
+                raise SchemaError(
+                    f"{name}: power pdu={pdu!r} is not a known kind:pdu file"
+                )
+            count = target["outlets"]
+            if outlet < 1 or outlet > count:
+                raise SchemaError(
+                    f"{name}: outlet {outlet} out of range 1..{count} on {pdu}"
+                )
+```
+
+- [ ] **Step 4: Wire `validate_power` into `generate` in `scripts/gen_rack.py`**
+
+Change the overlap loop so it also validates power. Replace:
+
+```python
+    if not errors:  # only check overlaps once placements are individually valid
+        for rack, ritems in racks.items():
+            try:
+                check_overlaps(ritems)
+            except SchemaError as e:
+                errors.append(f"{rack}: {e}")
+```
+
+with:
+
+```python
+    if not errors:  # only check overlaps once placements are individually valid
+        for rack, ritems in racks.items():
+            try:
+                check_overlaps(ritems)
+                validate_power(ritems)
+            except SchemaError as e:
+                errors.append(f"{rack}: {e}")
+```
+
+- [ ] **Step 5: Run to verify pass**
+
+Run: `pytest tests/test_gen_rack.py -q`
+Expected: PASS (all prior tests + 8 new).
+
+- [ ] **Step 6: Commit**
+
+```bash
+git add scripts/gen_rack.py tests/test_gen_rack.py
+git commit -m "feat(rack): validate power feeds against PDU outlets"
+```
+
+---
+
+### Task 2: `render_power` + page section (TDD)
+
+**Files:**
+- Modify: `scripts/gen_rack.py` (add `_node_id`, `render_power`; edit `render_page`)
+- Modify: `tests/test_gen_rack.py` (append tests)
+
+**Interfaces:**
+- Consumes: `_pdu_index` (Task 1), `render_page`, `generate`.
+- Produces:
+  - `_node_id(name: str) -> str` — hostname with non-alphanumeric chars replaced by `_`.
+  - `render_power(rack: str, items: list[dict]) -> str` — a fenced `mermaid` `flowchart LR` ending in a newline, or `""` when no item has a `power` feed.
+
+- [ ] **Step 1: Append failing tests to `tests/test_gen_rack.py`**
+
+```python
+def test_render_power_has_nodes_and_edge_labels():
+    items = [
+        item(hostname="pdu01", kind="pdu", rack_face="left", outlets=8),
+        item(hostname="mf00", rack_u=1, u_height=1, rack_face="front",
+             power=[{"pdu": "pdu01", "outlet": 3}]),
+    ]
+    out = gen_rack.render_power("rack01", items)
+    assert "```mermaid" in out
+    assert "flowchart LR" in out
+    assert "pdu01" in out
+    assert "8 outlets" in out
+    assert "outlet 3" in out
+    assert "mf00" in out
+
+
+def test_render_power_redundant_device_has_two_edges():
+    items = [
+        item(hostname="pdu01", kind="pdu", rack_face="left", outlets=8),
+        item(hostname="pdu02", kind="pdu", rack_face="right", outlets=8),
+        item(hostname="mf00", rack_u=1, u_height=1, rack_face="front",
+             power=[{"pdu": "pdu01", "outlet": 1},
+                    {"pdu": "pdu02", "outlet": 1}]),
+    ]
+    out = gen_rack.render_power("rack01", items)
+    assert out.count("-->|outlet") == 2
+
+
+def test_render_power_empty_when_no_feeds():
+    items = [item(hostname="mf00", rack_u=1, u_height=1, rack_face="front")]
+    assert gen_rack.render_power("rack01", items) == ""
+
+
+def test_render_power_is_deterministic():
+    a = item(hostname="pdu01", kind="pdu", rack_face="left", outlets=8)
+    b = item(hostname="mf01", rack_u=2, u_height=1, rack_face="front",
+             power=[{"pdu": "pdu01", "outlet": 2}])
+    c = item(hostname="mf00", rack_u=1, u_height=1, rack_face="front",
+             power=[{"pdu": "pdu01", "outlet": 1}])
+    assert gen_rack.render_power("rack01", [a, b, c]) == \
+        gen_rack.render_power("rack01", [c, b, a])
+
+
+def test_generate_includes_power_section(tmp_path):
+    hw = tmp_path / "hardware"
+    out = tmp_path / "out"
+    hw.mkdir()
+    _write_item(
+        hw,
+        "pdu01",
+        "---\nhostname: pdu01\nkind: pdu\nstatus: in-use\n"
+        "rack: rack01\nrack_face: left\noutlets: 8\n---\n",
+    )
+    _write_item(
+        hw,
+        "mf00",
+        "---\nhostname: mf00\nkind: server\nstatus: in-use\n"
+        "rack: rack01\nrack_u: 1\nu_height: 1\nrack_face: front\n"
+        "power:\n  - { pdu: pdu01, outlet: 1 }\n---\n",
+    )
+    rc = gen_rack.generate(hw, out)
+    assert rc == 0
+    page = (out / "rack01.md").read_text()
+    assert "## Power" in page
+    assert "```mermaid" in page
+    assert "outlet 1" in page
+```
+
+- [ ] **Step 2: Run to verify failure**
+
+Run: `pytest tests/test_gen_rack.py -q`
+Expected: FAIL — `AttributeError: module 'gen_rack' has no attribute 'render_power'`.
+
+- [ ] **Step 3: Add `_node_id` and `render_power` after `render_svg` in `scripts/gen_rack.py`**
+
+```python
+def _node_id(name: str) -> str:
+    """A mermaid-safe node id derived from a hostname."""
+    return re.sub(r"[^0-9A-Za-z]", "_", str(name))
+
+
+def render_power(rack: str, items: list[dict]) -> str:
+    """Return a mermaid power-distribution flowchart, or '' if no feeds."""
+    powered = [fm for fm in items if fm.get("power")]
+    if not powered:
+        return ""
+    pdus = _pdu_index(items)
+
+    edges: list[tuple[str, int, str]] = []
+    for fm in powered:
+        device = fm.get("hostname", "?")
+        for feed in fm["power"]:
+            edges.append((feed["pdu"], feed["outlet"], device))
+    edges.sort()
+
+    lines: list[str] = ["```mermaid", "flowchart LR"]
+    for pdu in sorted(pdus):
+        outlets = pdus[pdu].get("outlets")
+        lines.append(f'    {_node_id(pdu)}["{pdu}<br/>{outlets} outlets"]')
+    devices = sorted(
+        powered,
+        key=lambda i: (
+            i.get("rack_u", 0) if isinstance(i.get("rack_u"), int) else 0,
+            i.get("hostname", ""),
+        ),
+    )
+    for fm in devices:
+        device = fm.get("hostname", "?")
+        lines.append(f'    {_node_id(device)}["{device}"]')
+    for pdu, outlet, device in edges:
+        lines.append(
+            f"    {_node_id(pdu)} -->|outlet {outlet}| {_node_id(device)}"
+        )
+    lines.append("```")
+    return "\n".join(lines) + "\n"
+```
+
+- [ ] **Step 4: Insert the `## Power` section in `render_page` in `scripts/gen_rack.py`**
+
+In `render_page`, replace this block:
+
+```python
+    lines.append(f"![Rack {rack} elevation]({rack}-elevation.svg)")
+    lines.append("")
+    lines.append("## Occupancy")
+```
+
+with:
+
+```python
+    lines.append(f"![Rack {rack} elevation]({rack}-elevation.svg)")
+    lines.append("")
+    power = render_power(rack, items)
+    if power:
+        lines.append("## Power")
+        lines.append("")
+        lines.append(power.rstrip())
+        lines.append("")
+    lines.append("## Occupancy")
+```
+
+- [ ] **Step 5: Run to verify pass**
+
+Run: `pytest tests/test_gen_rack.py -q`
+Expected: PASS (all prior tests + 5 new).
+
+- [ ] **Step 6: Commit**
+
+```bash
+git add scripts/gen_rack.py tests/test_gen_rack.py
+git commit -m "feat(rack): render mermaid power graph into the rack page"
+```
+
+---
+
+### Task 3: Enable mermaid, populate provisional power data, regenerate
+
+**Files:**
+- Modify: `mkdocs.yml` (mermaid superfences fence)
+- Create: `docs/hardware/pdu01.md`, `docs/hardware/pdu02.md`
+- Modify: `docs/hardware/mf00.md`..`mf04.md` (add `power:`)
+- Regenerate: `docs/hardware/index.md`, `docs/infrastructure/racks/rack01.md`, `docs/infrastructure/racks/rack01-elevation.svg`
+
+**Interfaces:**
+- Consumes: `python3 scripts/gen_rack.py` / `make docs-index`, `mkdocs build --strict`, `make docs-check`.
+
+> **Operator note — provisional data.** The PDU placements and outlet assignments below are placeholders proving the feature, matching the existing fictional `mfNN` U positions. Replace with real values when known; `validate_power` will reject dangling/over-count feeds loudly.
+
+- [ ] **Step 1: Enable the mermaid custom fence in `mkdocs.yml`**
+
+In `mkdocs.yml`, replace the bare superfences line:
+
+```yaml
+  - pymdownx.superfences
+```
+
+with:
+
+```yaml
+  - pymdownx.superfences:
+      custom_fences:
+        - name: mermaid
+          class: mermaid
+          format: !!python/name:pymdownx.superfences.fence_code_format
+```
+
+- [ ] **Step 2: Create the two PDU files**
+
+Create `docs/hardware/pdu01.md`:
+
+```markdown
+---
+hostname: pdu01
+kind: pdu
+status: in-use
+rack: rack01
+rack_face: left
+outlets: 8
+---
+
+## Notes
+
+- Provisional placeholder PDU (left rail). Outlet assignments are not yet real.
+```
+
+Create `docs/hardware/pdu02.md`:
+
+```markdown
+---
+hostname: pdu02
+kind: pdu
+status: in-use
+rack: rack01
+rack_face: right
+outlets: 8
+---
+
+## Notes
+
+- Provisional placeholder PDU (right rail). Provides redundant feeds.
+```
+
+- [ ] **Step 3: Add `power:` to the five host files**
+
+In `docs/hardware/mf00.md`, add to the frontmatter (before the closing `---`) — note mf00 has **two** feeds (the redundant demonstration):
+
+```yaml
+power:
+  - { pdu: pdu01, outlet: 1 }
+  - { pdu: pdu02, outlet: 1 }
+```
+
+In `docs/hardware/mf01.md` add:
+
+```yaml
+power:
+  - { pdu: pdu01, outlet: 2 }
+```
+
+In `docs/hardware/mf02.md` add:
+
+```yaml
+power:
+  - { pdu: pdu01, outlet: 3 }
+```
+
+In `docs/hardware/mf03.md` add:
+
+```yaml
+power:
+  - { pdu: pdu01, outlet: 4 }
+```
+
+In `docs/hardware/mf04.md` add:
+
+```yaml
+power:
+  - { pdu: pdu01, outlet: 5 }
+```
+
+- [ ] **Step 4: Regenerate all indices and rack artifacts**
+
+Run: `make docs-index`
+Expected: `gen_overview.py` rewrites `docs/hardware/index.md` (now listing pdu01/pdu02 under "PDUs"); `gen_rack.py` prints `Wrote rack01.md + rack01-elevation.svg (7 item(s))`.
+
+- [ ] **Step 5: Confirm the generated page has a rendered power graph and PDU rails**
+
+Run: `grep -c "outlet" docs/infrastructure/racks/rack01.md`
+Expected: ≥ 6 (one edge per feed: mf00 ×2, mf01..mf04 ×1).
+
+Run: `grep -c "pdu0" docs/infrastructure/racks/rack01-elevation.svg`
+Expected: ≥ 2 (pdu01 + pdu02 drawn as side-rails).
+
+- [ ] **Step 6: Run the full test suite**
+
+Run: `make test`
+Expected: PASS (all tests).
+
+- [ ] **Step 7: Build the site strictly**
+
+Run: `mkdocs build --strict`
+Expected: build succeeds with no warnings-as-errors; `site/infrastructure/racks/rack01/index.html` contains a `<pre class="mermaid">` (or `<div class="mermaid">`) block rather than a plain `<code>` fence.
+
+Verify: `grep -c "mermaid" site/infrastructure/racks/rack01/index.html`
+Expected: ≥ 1.
+
+- [ ] **Step 8: Confirm the drift guard is satisfied**
+
+Run: `make docs-check`
+Expected: exit 0 — committed artifacts match a fresh regeneration.
+
+- [ ] **Step 9: Commit**
+
+```bash
+git add mkdocs.yml docs/hardware/ docs/infrastructure/racks/
+git commit -m "feat(rack): enable mermaid, populate provisional power data"
+```
+
+---
+
+## Self-Review
+
+**Spec coverage (`2026-06-24-rack-power-design.md`):**
+- `power:` frontmatter on devices — Task 3 (populate); validated Task 1. ✔
+- PDU files (`kind: pdu`, `outlets`, 0U `left`/`right`) — Task 3; outlets validated Task 1. ✔
+- Validation rule 3 (pdu resolves to kind:pdu; outlet in range; pdu declares outlets) — Task 1 (`validate_power`), wired into `generate`. ✔
+- Mermaid power graph, outlet as edge label, redundancy as two edges, omit-when-empty, deterministic — Task 2 (`render_power`), inserted in `render_page`. ✔
+- Node-id sanitization — Task 2 (`_node_id`). ✔
+- Mermaid pulled forward in `mkdocs.yml` — Task 3 Step 1. ✔
+- No Makefile/CI/overview_config changes — honored (Global Constraints); drift covered by existing `racks/` diff — Task 3 Steps 4/8. ✔
+- Provisional data (pdu01 left → mf00..mf04 o1..o5; pdu02 right → mf00 o1) — Task 3 Steps 2–3. ✔
+
+**Placeholder scan:** No "TBD"/"handle edge cases"/"similar to Task N". The only operator-judgement item is provisional power values, explicitly bounded and guarded by `validate_power`.
+
+**Type consistency:** `_pdu_index` → `dict[str, dict]`; `validate_power`/`check_overlaps` → `None` (raise `SchemaError`); `render_power`/`render_page`/`render_svg`/`_node_id` → `str`; `generate` → `int` (0/1). `validate_power(ritems)` is called per-rack alongside `check_overlaps(ritems)`. `render_power` consumes `_pdu_index` and feeds `render_page`. Names match across tasks and tests.